Showing papers on "Hyperpolarizability published in 1995"

Chiral metal complexes with large octupolar optical nonlinearities

Abstract: OPTICALLY nonlinear organic materials show considerable potential for applications in optical signal processing and telecommunications1,2. Most materials are based on the p-nitro-aniline template, in which the optical nonlinearities are intimately associated with quasi-one-dimensional charge transfer. But there are problems associated with this conventional approach, arising from the strongly dipolar nature of the molecules2. It has recently been recognized3–5 that two- and three-dimensional stereochemistry offers new possibilities for the design and synthesis of optically nonlinear molecules, in which charge transfer is multidirectional rather than dipolar in character; octupolar nonlinearities have now been demonstrated in several molecular systems5–7. Tri-substituted ruthenium complexes6 appear particularly attractive because intense, multidirectional metal-to-ligand charge transfer leads to a significant enhancement of the optical nonlinearity, as quantified by the quadratic hyperpolarizability, β. Here we show that the choice of ligand can further increase β to values in excess of 10-27e.s.u., comparable to the best dipolar optically nonlinear molecules.

Size-consistent approach and density analysis of hyperpolarizability: Second hyperpolarizabilities of polymeric systems with and without defects

Abstract: Various size‐consistent approaches to the calculation of molecular hyperpolarizabilities are analyzed based on the double perturbation theory. General equations for the nth‐order response property with respect to an external time‐independent field are derived on the basis of the Rayleigh–Schrodinger perturbation theory (RSPT) and the coupled‐cluster (CC) theory. The corresponding equations for the time‐dependent case are also derived by the CC formalism, which is referred to as the time‐dependent CC (TDCC) method. In order to clarify the spatial characteristics of polarizability and hyperpolarizability, we present an analysis method using a new concept ‘‘the polarizability and hyperpolarizability densities.’’ As an application of the size‐consistent methods, the static second hyperpolarizabilities (γ) of π‐conjugated polymeric systems are calculated by the use of the uncoupled (UCHF), and coupled‐Hartree–Fock (CHF) methods combined with the semiempirical INDO approximation. Characteristics of γ values cal...

Supramolecular Second-Order Nonlinearity of Polymers with Orientationally Correlated Chromophores

Abstract: Nonlinear optical chromophores can be organized as orientationally correlated side groups of polymers with a rigid backbone. In such an organization, each chromophore contributes coherently to the second-order nonlinear response of the polymer structure. A first hyperpolarizability exceeding 5000 × 10−30 electrostatic units was measured for a poly(isocyanide) structure containing ∼100 chromophores by means of hyper-Rayleigh scattering. Electric field-induced second-harmonic generation measurements confirmed that the product of the permanent dipole moment and the first hyperpolarizability was enhanced for the polymer structure. These results provide guidelines for future efforts to optimize supramolecular structures for applications in second-order nonlinear optics.

Hydrazone Derivatives, an Efficient Class of Crystalline Materials for Nonlinear Optics

Abstract: We report on the synthesis and optical characterization of hydrazone derivatives developed for second-order nonlinear optics. Electric-field-induced second harmonic generation (EFISH) as well as semiempirical quantum-chemical computations have been carried out to investigate and explain the nonlinear optical properties of these molecules. We obtained values of up to 220 x 10(-40) m(4)/V for the molecular hyperpolarizability beta at lambda = 1907 nm. The investigation of a series of 39 hydrazone derivatives with the second harmonic generation powder test according to Kurtz and Ferry revealed that an extraordinarily large fraction of these hydrazones show efficient second-order nonlinear activity. Among them, 4-(dimethylamino)-benzaldehyde-4-nitrophenylhydrazone (DANPH) and 4-(1-azacycloheptyl)-benzaldehyde-4-nitrophenylhydrazone (ACNPH) were selected for more detailed investigations. Their crystalline structures are presented, and the role played by hydrogen bonds in their molecular packing is emphasized. Finally, preliminary linear and nonlinear optical data of DANPH crystals are reported. [References: 42]

Ab initio finite oligomer method for nonlinear optical properties of conjugated polymers. Hartree-Fock static longitudinal hyperpolarizability of polyacetylene

Abstract: Ab initio restricted Hartree–Fock 6‐31G calculations are reported for the static longitudinal hyperpolarizability of the linear polyenes C4H6 through C44H46. Using a new extrapolation technique the infinite chain value in polyacetylene is determined with an accuracy similar to that achieved for small molecules. This is the first in a series of articles leading to a comprehensive ab initio treatment for the nonlinear optical properties of conjugated polymers.

Sign change of hyperpolarizabilities of solvated water

Abstract: The experimental work by Levine and Bethea [J. Chem. Phys. 65, 2429 (1976)] and by Ward and Miller [Phys. Rev. A 19, 826 (1979)] on the hyperpolarizability of solvated water and water in the gas phase, respectively, showed a very substantial effect of the solvent on the measured hyperpolarizability. The sign of the hyperpolarizability of solvated water changed compared to gas phase and the numerical value increased by a factor of 1.5. This article presents a theoretical investigation of the solvent effects of the hyperpolarizabilities and their frequency dispersions for liquid water using the continuum, semicontinuum, and supermolecular models. Calculations involving the semicontinuum and supermolecular models give the sign change of the hyperpolarizabilities, indicating that the hydrogen bonds and the static dipole interaction have substantial impact on the hyperpolarizability of liquid water. Hyperpolarizabilities calculated by the supermolecular approach are about one third of those calculated by the semi‐continuum model. The continuum and semicontinuum models involve a recent implementation of a quantum mechanical reaction field response method.

Effect of Molecular Polarization on Bond-Length Alternation, Linear Polarizability, First and Second Hyperpolarizability in Donor-Acceptor Polyenes as a Function of Chain Length

Abstract: The linear (α) and nonlinear (β, γ) molecular polarizabilities of a series of donor-acceptor polyenes containing 3-8 π-bonds are studied using the semiempirical AMl parametrization and finite-field (hyper)polarizability computations as a function molecular polarization and resulting changes in bond-length alternation. Plots of α, β, and γ versus bond length alternation had similar shapes (although different magnitudes) for each chain length. The changes in α, β, and γ with molecular length were fit to exponential functions (N^m) for various bond-length alternations. These values varied over a significant range depending upon the value of bond-length alternation chosen.

Solvent effects on first-order molecular hyperpolarizability: a study based on vibrational observables

Abstract: Using a recently developed method, we show here that solvent effects on the first molecular hyperpolarizabilities of push‐pull polyenes can be predicted by evaluation of the relaxation contribution βr to the hyperpolarizability from vibrational infrared and Raman intensities and vibrational frequencies. The molecules studied in this work are a few organic polymethine dyes with different donor and acceptor groups. The analysis of their vibrational spectra confirms the key role played by the structural parameters of the polyene chain in determining the nonlinear optical response.

Langmuir Film-Forming and Second Harmonic Generation Properties of Lanthanide Complexes

Abstract: A series of amphiphilic lanthanide complexes were designed and synthesized, in which the lanthanide complex anions act both as the counterions of hemicyanine and as the spacer within a Langmuir-Blodgett (LB) film. Studies on the surface pressure-area ({pi}-A) isotherms of these complexes show that the film-forming properties can be clearly improved if appropriate {Beta}-diketone ligands were chosen. The effects of molecular structures of the complexes, including the variation of lanthanide central ions, the structures of {Beta}-diketone ligands, and the length of alkyl chains in hemicyanines, on the film-forming properties of the materials are discussed. From second-harmonic generation experiments, the largely enhanced second-order molecular hyperpolarizability of lanthanide complexes with good film-forming properties were obtained compared with the hemicyanine iodide. This effect may be due in part to the local field effect but primarily molecular ordering and ordered segregation of hemicyanine chromophores by the bulky lanthanide complex anions. The charge separation of the hemicyanine chromophores was supported by the crystal structure of a model complex. The homogeneity of the film was verified by low angle X-ray diffraction and also by the linear relationship of the absorbance vs the number of layers of the LB films of a selected complex. 37 refs., 7more » figs., 3 tabs.« less

Third‐order nonlinear optical response in a multilayered phthalocyanine composite

Abstract: The third‐order nonlinear optical properties of multilayered films containing 23% by weight of an axially modified silicon phthalocyanine derivative have been measured by degenerate four‐wave mixing at 532 nm with 70 ps full width at half maximum pulses. The average χ(3)of the films measured at (1.33±0.15) ×10−11 esu using CS2 as a standard and the cubic hyperpolarizability 〈γ〉 was calculated at (1.97±0.22)×10−32esu. The degenerate four‐wave mixing signal profile indicates that the films have a response time better than 70 ps.

Nonlinear optical materials with reduced aromaticity and bond length alternation

Abstract: Compositions for use in non-linear optical devices. The compositions have high first molecular electronic hyperpolarizability (β) and therefore display high second order non-linear optical properties when incorporated into non-linear optical devices. The acceptor and donor groups which are used in the compositions, along with the π(pi)-bridge length is chosen to optimize second-order non-linear optical responses.

Ab initio studies of the dipole polarizabilities of conjugated molecules: Part 5. The five-membered heterocyclics C4H4E (E = BH, AlH, CH2, SiH2, NH, PH, O and S)

Abstract: We report high quality ab initio calculations of the geometries, the static dipole polarizability and the first hyperpolarizability of the electronic ground state for a series of five-membered conjugated heterocyclics C4H4E, E = BH, AlH, CH2, SiH2, NH, PH, O and S (borole, aluminocyclopentadiene, cyclopentadiene, silacyclopentadiene, pyrrole, phosphole, furan and thiophene, respectively). The geometries, fully optimized at HF/6-31G∗∗ level of theory, show good agreement with reported experimental and/or other theoretical ones. Changes induced by the heteroatom on the structural and electronic properties of these C4H4 rings are explained in terms of the heteroatom electronegativity. The sensitivity of the polarizability calculations to the variation of basis set was studied. We show that increasing the number of multiple d and p polarization functions in the 6-31 + G(nd, mp) basis set at Hartree-Fock level leads to values of the polarizability tensor components that are in good agreement with available experimental data. Electron correlation effects on the static dipole polarizability are shown to be non-negligible, when calculated at the MP2/6-31 + G(d,p) level of theory for borole, cyclopentadiene, pyrrole, furan and thiophene. We find that the calculated average dipole polarizability of these molecules is linearly related to the bond distance “a” C-E of the C4H4E ring with a correlation coefficient of r2 = 0.98, by α ave 10 −40 CV −1 m 2 = 1.523 + 4.973a a 0 with phosphole being an exception; this compound shows an enhanced and anomalous polarizability with respect to the rest of the series. In addition, we show that these polarizabilities can be used as an aromaticity scale for explaining the known aromaticity in compounds such thiophene, pyrrole and furan. We also give the first-ever high quality calculation at the HF/6-31 + G(3d,3p) level of theory for the first hyperpolarizability tensors of these molecules.

Hyper‐Rayleigh scattering studies of first order hyperpolarizability of tricyanovinylthiophene derivatives in solution

Abstract: First order hyperpolarizabilities, β, for donor–acceptor substituted heteroaromatic compounds are measured by the hyper‐Rayleigh scattering technique. Hyper‐Rayleigh scattering utilizes the mechanism of number density fluctuations and enables the second harmonic generation signal of nonlinear optical chromophores to be generated as scattered light. Effects of substituting different electron donating groups to the parent heteroaromatic compounds and different solvents on the hyperpolarizability is investigated using this technique.

Abinitio polarizability study of polypyrrole

Abstract: The longitudinal polarizability, αzz, and second order hyperpolarizability, γzzzz, of the (C4H3N)RH2 oligopyrroles, where R=1−9, are determined at the Hartree–Fock (HF) level of theory using a 6‐31G basis set. The effect of electron correlation is taken into account using Moller–Plesset perturbation theory through second order for the R=1−5 oligopyrroles. Methods for extrapolation to the infinite polymer values are explored. The convergence behavior of the correlated results as a ratio with the corresponding HF values may indicate that a scaled HF procedure could be appropriate for finding correlated estimates to the infinite polymer property values. We also propose a generalized finite field recipe which can easily be used in conjunction with popular black‐box electronic structure programs for determining molecular polarizabilities through second order. The αzz and γzzzz values obtained from using this procedure on a variety of polyacetylene and polypyrrole oligomers are in excellent agreement with those...

Molecular crystals and polymers for nonlinear optics

Abstract: We present new experimental results on second-harmonic generation in highly conjugated organic molecules and molecular crystals recently developed in our group, as well as on electro-optic eftects in thin-film polymers. A large value of the molecular hyperpolarizability of a new hydrazone-type molecule crystallizing in a noncentrosymmetric point group is reported. Large nonlinear optical coefticients of up to 840 ± 200 pmN were measured in crystals of 4'-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). The new experimental results are compared with theoretical calculations of limiting values of nonlinear optical coefticients. Computer modeling of crystal structures shows good agreement with experimental results. Measurements on electro-optic polymers with high thermal stability are presented.

Analysis of the Large Hyperpolarizabilities of Push-Pull Quinonoid Molecules

Abstract: Donor-acceptor substituted quinonoid molecules have been investigated very tittle in connection with nonlinear optical (NLO) applications. We present a theoretical analysis of the hyperpolarizability, β, of a model push-pull quincnold molecule as a function of the quinonoid-benzenoid character (QBC). β is found to be quite large at all geometries except the quinonoid extreme; it results from appreciable contributions from a large number of excited states.

Quadratic non-linear optical properties of some donor–acceptor substituted thiophenes

Abstract: A series of thiophenes and bithiophenes containing combinations of dimethylamino and dimethylhydrazono π-donor and nitro and dicyanovinyl π-acceptor groups was synthesized in order to study their non-linear optical properties. Solution molecular hyperpolarizabilities were determined by a combination of experimental dipole moments and results from the electric field induced second harmonic generation experiment. Values obtained correlate well with those calculated by the CNDOVSB molecular orbital method. The main structure-property relationships deduced from the results are: (i) thiophene provides a more efficient electron delocalization pathway than benzene; (ii) this increase is proportionately even greater for bithiophene compared with biphenyl; (iii) dimethylhydrazono results in twice the hyperpolarizability of dimethylamino in a comparable molecule; and (iv) dicyanovinyl is a more effective electron acceptor group than nitro in the thiophenes synthesized and calculated.

Electron density study by X-ray and neutron diffraction of an NLO compound: N-(4-nitrophenyl)-l-prolinol. Description of quadratic hyperpolarizability

Abstract: The study of the electron density and the determination of the dipolar moment of the molecule in the crystalline compound N-(4-nitrophenyl)-L-prolinol have been completed using X-ray and neutron diffraction. The deformation maps and the calculations of the atomic net charges demonstrate the character of the donor-acceptor couple (DA) linked to the phenyl transmitter. The dipolar molecular moments obtained by several methods have similar values, except the method of kappa refinement. The kappa refinement appears inadequate to solve the phase problem. Accurate knowledge of the first molecular moment reduces the ambiguity on the quadratic polarizability coefficient β, measured from electric field-induced second-harmonic generation (EFISHG).The coefficients of the cubic moment (third-order semi-invariant) of the electronic distribution in the crystal state are compared with those of the quadratic hyperpolarizability obtained by theoretical calculations. An estimate of relevant coefficients in octupolar-type material would provide guidance to the choice of systems for non-linear optics. Crystal data: C 11 H 14 N 2 O 3 , M r , = 222.2, monoclinic, P2 1 , Z = 2, F(000) = 236, T = 122 K, a = 5.152 (4), b = 14.790 (3), c = 7.134 (2) A, β = 106.14 (4)°, V = 522.18 A 3 , D x = 1.41 Mg mm -3 at 122 K, μ = 0.084 mm -1 for λ = 0.7107 A

Ka Values of Weak Organic Acids in Protic Solvents Obtained from Their First Hyperpolarizabilities in Solution

Abstract: The first hyperpolarizabilities (beta) of some weak aromatic organic acids have been measured in protic solvents by the hyper-Rayleigh scattering (HRS) technique at low concentrations. The measured hyperpolarizability (beta(m)) varies between the two extreme limits: the hyperpolarizability of the acid form (beta(HA)) at the lower side and that of the basic form (beta(A-)) at the higher side. The degree of dissociation (alpha) of the acid in a solvent is related to the measured hyperpolarizability, beta(m), by the following relationship: beta(m)(2)=(1-alpha)beta(HA)(2)+alpha beta(A-)(2). The calculated beta's including solvent effects in terms of an Onsager field do not reproduce the experimentally measured hyperpolarizabilities. Other solvent-induced effects like hydrogen bonding and van der Waals interactions seem to influence the first hyperpolarizability and, thus, indirectly the extent of dissociation of these weak acids in these protic solvents.

Theoretical investigation of the electronic properties of donor-acceptor n-benzylideneanilines and related molecules

Abstract: The dipole moments, transition energies and hyperpolarizabilities of a substituted stilbene, azobenzene and two isomeric–benzylideneanilines containing the 4-dimethylamino-group at one end of the molecule and the 4-nitro-group at the other, have been calculated using a semi-empirical sum-over-states method on structures optimized with the 3-21G basis set. An excellent correlation is found between the calculated and experimental spectra. The azobenzene is predicted to have the largest hyperpolarizability of this series of molecules, followed by the stilbene and N-(nitrobenzylidene)aniline which have comparable values, with the non-planar N-(benzylidene)nitroaniline showing the smallest value.

Defeating tradeoffs for nonlinear optical chromophores

Abstract: Materials to be used for optoelectronic, photorefractive, or frequency doubling applications must have high nonlinearities, good thermal stabilities, and low optical loss (high transparency). Organic compounds synthesized for incorporation into poled nonlinear polymers typically exhibit tradeoffs between nonlinearity and each of the other two qualities. By judicious use of arylamino donor groups and cyano-containing acceptor groups, a small set of chromophores that are both highly nonlinear and stable at high temperatures has been prepared. By selecting delocalized bridging moieties that are either tuned for optimum hyperpolarizability or exhibit two charge-transfer excited states, highly transparent chromopohores with excellent nonlinearities can be prepared. The results suggest that thermal stability and nonlinearity are jointly achieved by modifying donor and acceptor groups, while transparency and nonlinearity are jointly achieved by modifying bridging groups.

Molecular softness, hypersoftness, infrared absorption, and vibrational raman scattering: new relations derived from nonlocal polarizability densities

Abstract: This work rigorously relates electromagnetic properties and characteristics of molecular potential energy surfaces to the empirical concept of ‘‘softness,’’ used to categorize Lewis acids and bases, and to summarize observed patterns of reactivity. New equations are derived that connect infrared absorption intensities, vibrational force constants, intermolecular forces at first order, and linear electric‐field shielding tensors to softness kernels as defined in density functional theory. A generalization to nonlinear response—by introduction of the hypersoftness—leads to new equations in density‐functional terms for vibrational Raman band intensities, the cubic anharmonicities in molecular potential energy surfaces, intermolecular forces at second order, and nonlinear electric‐field shielding tensors. The analysis employs relations of the softness and hypersoftness to nonlocal polarizability and hyperpolarizability densities that represent the intramolecular distribution of response to inhomogeneous electric fields.